JP5926419B1 - Phase loss detector - Google Patents

Abstract

An open phase detector capable of accurately detecting an open phase state is provided. The phase failure state determination unit (8) always has the [first condition] that the absolute value of the vector quantity of the same "one phase" is equal to or less than K1 times the absolute value of the vector quantity of the other phase. [Second condition] that the vector sum of the fundamental wave components of the other two-phase currents is substantially zero, and the current vector of the phase in which the absolute value of the current vector quantity is the maximum among the three phases. For the [third condition] that the absolute value of the quantity is 50% or more of the charging current value including the exciting current of the transformer, it is determined every M cycles, and the [first condition], [ When the [second condition] and [third condition] are satisfied, it is determined that "one phase" is in a positive open phase state. The M value setting unit (7c) increases the value of M as the effective value of the phase having the maximum effective value among the three phases for each of the N current waveform data is increased, while the effective value is maximized. The larger the effective value of the phase, the smaller the value of M. [Selection] Figure 1

Description

  The present invention relates to an open phase detector, and more particularly, relates to an open phase detector that is installed at a power receiving point on a primary side of a transformer connected to a transmission line or a distribution line and monitors an open phase state of a three-phase power source. More specifically, the present invention relates to an open phase detector that can correctly detect open phase even when a load is not connected to the secondary side of the transformer.

  Basically, when only one phase of the three-phase current is close to zero ampere, it is called a one-phase open phase, and when the load is an induction motor, a reverse-phase current flows when one phase is missing. It stops and it generates heat. In this case, the healthy phase is an overcurrent for the induction motor, but it is not as large as the inrush current when the breaker is turned on, not a short-circuit accident, so it cannot be shut off by the breaker, and a dedicated detector for overcurrent protection is required. is there. Therefore, a dedicated breaker with a phase loss detection function is commercially available. In addition, motor drive inverters and the like having a phase loss detection function are commercially available.

  However, if the load is an emergency power supply unit that is installed in a substation and is not usually used, if the secondary side of the transformer is unloaded, the primary side even in a healthy phase that is not in a phase failure state The excitation current is very small, such as the excitation current, especially in power transformers designed exclusively for emergency power supplies, the excitation current at no load is designed to be reduced to about 0.1% or less of the rated current. There is something that has been. Moreover, the current detection current transformer installed on the primary side of the transformer needs to convert the current at the time of steady state or short circuit accident and transmit it to a relay or other measuring instrument, so that the current transformation ratio is 800: Designed to a high ratio such as 1. In such a case, the normal current value is about 0.1 A, and the output of the current transformer is about several hundred μA. When the output of such a current transformer is sent to a relay room in a substation building several hundred meters away via a cable and measured in the relay room, it is affected by inductive noise and so on. Phase detection was difficult.

  Conventionally, as the phase loss detector, for example, Patent Document 1 (Patent No. 4655207), Patent Document 2 (Japanese Patent Laid-Open No. 2005-261157), and Patent Document 3 (Japanese Patent Laid-Open No. 2003-302434) have been described. Some use the phase loss detection method.

Patent No. 4655207 JP 2005-261157 A JP 2003-302434 A

  A conventional phase loss detection method will be described below.

  In Patent Document 1 (Patent No. 4655207), when detecting a disconnection of a distribution line on the load side of an accident point, a three-phase voltage signal is measured, and a stable phase change in which an apparent phase change due to a fine ground fault is suppressed. A method is described in which a simple disconnection accident is detected and a fine ground fault and a disconnection accident can be distinguished.

  Further, Patent Document 2 (Japanese Patent Laid-Open No. 2005-261157) describes a phase loss detection technique that reduces costs by detecting phase loss detection of a three-phase current with two current transformers. .

  Further, Patent Document 3 (Japanese Patent Application Laid-Open No. 2003-302434) describes that data is averaged in order to reduce erroneous determination in phase loss detection of a three-phase current.

  However, in the phase loss detection method described in Patent Document 1 described above, when another power source is connected to the secondary side of the transformer, or the primary side of the transformer is Y-connected and the secondary side is Δ-connected and light. When it is a load, even if the primary side of the transformer is open, almost normal voltage appears at the transformer terminal due to the line voltage generated at the △ connection on the secondary side. There is.

  For example, as shown in FIG. 9, if the power supply wiring on the primary side of the transformer is disconnected by one line, the phase will be in an open phase, but if the secondary side is unloaded and Δ connected, Since the reverse phase voltage of about the normal voltage value is generated by the healthy phase voltage, it cannot be said that the voltage of the phase that is in the open phase state is necessarily reduced. Therefore, phase loss detection is insufficient only by voltage signal observation.

  In the case of transformers at substations and power plants, if the primary side is Y-connected, the neutral point is often grounded. In many cases, the secondary side of the transformer is a △ connection system. Therefore, even if one phase is broken on the primary side of the transformer and the phase is lost, if the secondary side of the transformer is in no load or close to no load, the vector sum of the other two-phase voltages is missing in reverse polarity. Since it is applied to the secondary side of the phases that are in phase, a voltage of approximately the same level as the normal voltage appears on the primary side regardless of the phase loss state.

  On the other hand, in the phase loss detection method described in Patent Document 2, when the secondary side of the transformer is in an unloaded state and the measured value itself is minute and there are many noise components such as induction noise, the phase loss state is erroneously determined. There is a possibility to do. For example, in the case of white noise, as in the case of the phase loss detection method described in Patent Document 3 above, it can be solved by data averaging. However, as in the case of inductive noise, the noise waveform itself is a commercial frequency vector. If you have a quantity, averaging does not solve it.

  Also, when the load is connected to the secondary side of the transformer, there is no problem because the load current is larger than the noise component, but the aim of the present invention is to detect the phase loss even when the load is not connected. . The reason is as follows.

  In general, if the secondary side of the transformer is in an unloaded state, there is no real harm even if the primary side is in a phase-open state. However, in the case of emergency power supply equipment, voltage imbalance occurs immediately when a load is connected in an emergency with no load, and if the load is an induction machine, a negative phase component similar to the positive phase component occurs. To do. If this happens, the rotor will generate heat without rotation and will burn out if left as it is. In such a case, this emergency power supply facility must be stopped. This makes no sense as an emergency facility. Therefore, the phase loss detector used in such emergency equipment can be used even in a normal no-load state, and is meaningless unless it can detect the phase loss state before being connected to the load.

  Therefore, in the present invention, when a load is not connected to the secondary side of the transformer, when a separate power source is connected, and when a white noise component or an inductive noise component is superimposed on the signal cable of the measurement circuit Even so, an object of the present invention is to provide a phase loss detector capable of accurately detecting the phase loss state.

In order to solve the above problems, the phase loss detector of the present invention is:
A / D conversion is performed on a signal representing three-phase current on the primary side of a transformer connected to a transmission line or distribution line at a sampling frequency corresponding to N (N is a positive integer) per cycle at a commercial frequency. An A / D converter;
A vector amount calculation unit for calculating a current vector amount of each phase on the primary side of the transformer from the current waveform data of each phase A / D converted by the A / D converter;
Based on the current waveform data of each phase, an effective value calculation unit that calculates an effective value of each phase for each of the N or N multiple times the current waveform data;
A phase loss state determination unit for determining a phase loss state on the primary side of the transformer based on the calculation result of the vector amount calculation unit;
The vector quantity calculation unit is
A Fourier transform operation is performed over the current waveform data of each phase for M cycles (M is a positive integer) at the commercial frequency, and the magnitude of the fundamental wave component of the current of each phase on the primary side of the transformer A vector quantity consisting of a phase angle is extracted every M cycles,
The phase loss state determination unit is
In the vector quantity of the fundamental wave component of the current of each phase for the M cycles extracted by the vector quantity calculation unit, the absolute value of the same "1 phase" vector quantity among the three phases is the vector of the other phase. A first condition that the absolute value of the quantity is equal to or less than K1 times (K1 is a constant close to zero less than 1.0, for example, about 0.03);
When the neutral point on the primary side of the transformer is ungrounded, the vector sum of the fundamental wave components of the other two-phase currents is substantially zero, or the neutral point on the primary side of the transformer When the point is grounded via a ground line, a second condition that the vector sum of each of the currents of the two phases and the current of the ground line is substantially zero;
Charging the absolute value of the vector of the phase of the current absolute value of the vector of current among the three phases is in the maximum, including the exciting current of the normal time in the primary side any one phase of the transformer The third condition that the current value is about 50% or more is determined every M cycles, and the first, second, and third conditions are continuously set L times (L is a positive integer) continuously. When satisfying the above, it is determined that the above-mentioned “one phase” is in an open phase state, and
For each of the N current waveform data calculated by the effective value calculation unit, the value of M is set to a larger value as the effective value of the phase having the maximum effective value among the three phases decreases. An M value setting unit is provided for setting the M value to a smaller value as the effective value of the phase having the maximum effective value is larger.

  When the secondary side of the transformer connected to the power transmission line or distribution line is in the no-load state, detection of the open phase on the primary side is difficult due to the small current, but before the load is connected and the transformer is in use. Since it only needs to be able to be detected, there is a feature that sufficient time is taken to detect the phase loss state. The present inventor has devised a phase loss detector capable of detecting phase loss with high accuracy by using this feature and detecting a sufficient amount of time with a minute current.

  Based on this concept, the inventor of the present invention has installed a voltage (550 kV) and a current (about 0.1 A) at the time of no-load of an emergency power transformer installed at a distance of about 200 m. Observe through voltage transformer (VT) and current transformer (current transformation ratio 800: 1) and its secondary cable (about 200m or more), collect data for up to about 3000 cycles of AC waveform, and in the substation By removing the white noise component generated in step 1, it was possible to realize a phase loss detector that can determine whether or not the phase loss state is more accurate.

  In addition, using the same concept, the micro-harmonic component included in the excitation current due to the hysteresis characteristics of the transformer normally flows from the primary circuit of the transformer toward the power supply side. The impedance of the power supply can be measured, but the value increases if it is disconnected. Therefore, by measuring the impedance on the power supply side over a long period of time, even if the signal itself is small, the secondary side of the current transformer We thought that the presence or absence of disconnection on the primary side of the transformer could be correctly determined even when the white noise component or electromagnetic induction noise component was on the signal line.

  In the present invention, when the secondary side of the transformer is unloaded, the waveform is observed over a relatively long time (for example, about 10 seconds to 1 minute) by setting the M value to a large value. The presence / absence of a phase state is detected. When a load is connected, an open phase state can be easily detected in a short time with a larger load current, so the M value is set to a small value. In such a case, it must be able to be determined in a short time, but since the current is large and the ratio of the observed waveform to the error of the instantaneous value (referred to as the S / N ratio) increases, it can be determined in a short time measurement.

  According to the above configuration, when a load is not connected to the secondary side of the transformer, when a separate power source is connected, and when a white noise component or inductive noise component is superimposed on the signal cable of the measurement circuit Even so, the phase loss state can be accurately detected.

In the phase loss detector of one embodiment,
In the phase loss state determination unit, the constant K1 used for the first condition is about 0.03.

  According to the embodiment, the phase loss state determination unit can detect the phase loss state more accurately by setting the constant K1 used for the first condition to about 0.03.

In the phase loss detector of one embodiment,
A determination result output unit is provided that displays at least one of the determination result of the phase loss state determination unit and the transmission to the outside.

  According to the above embodiment, since the determination result output unit displays at least one of the determination result of the phase loss state determination unit or the transmission to the outside, it is possible to notify the accurate detection result of the phase loss state.

In the phase loss detector of one embodiment,
The A / D converter is
A / D conversion is performed on a signal representing three line voltages on the primary side of the transformer at a sampling frequency corresponding to N per cycle at the commercial frequency,
The vector quantity calculation unit is
A Fourier transform operation is performed from the line voltage waveform data A / D converted by the A / D converter to the line voltage waveform data for M cycles at the commercial frequency, and the primary side of the transformer Extracting the vector quantity consisting of the magnitude and phase angle of the fundamental wave component and third to seventh harmonic components of each line voltage,
Any of the third to seventh harmonic components based on the fundamental wave component of each line voltage and the third to seventh harmonic component vector quantities obtained by the vector quantity calculation unit. A line impedance vector amount calculation unit for calculating three line impedance vector amounts as viewed from the primary side of the transformer from one to the power source side for each M cycles,
The phase loss state determination unit is
Of the three line impedance vector quantities calculated by the line impedance vector quantity calculation unit, the absolute value between the lines with the next largest absolute value is K2 times (K2 is the absolute value between the lines with the smallest absolute value). And the first, second, third, together with a fourth condition that a common phase included between two lines having a large absolute value is in an open phase state. When the condition is determined every M cycles and the first, third, and fourth conditions are satisfied and the second condition is not satisfied for L consecutive times, the “one phase” is positively missing. Determined to be in phase state.

  Here, the line impedance vector quantity is an impedance vector quantity on a plane coordinate having the resistance component of the line impedance as the X axis and the reactance component as the Y axis.

  According to the above embodiment, when the first condition for the phase loss determination and the third condition for the operation determination are satisfied but the second condition where the sum of the current vector amounts is zero is not satisfied, the line impedance vector amount calculation unit The line between which the absolute value is the smallest among the three line impedance vector quantities calculated by (between a pair of healthy lines that are not broken) is the line with the next largest absolute value (the phase that has lost phase) When the absolute value of the two lines (including two lines) is greater than or equal to K2 times (K2 is a constant exceeding 1.0), the common one phase included between the two lines with a large absolute value is an open-phase state. The fourth condition of being in the above can complement the determination of the presence / absence of the phase loss state, and enables more reliable detection.

  The phase loss detector of this embodiment is intended to detect a minute excitation current by observing for a long time, but although the random noise generated in the signal line on the secondary side of the current converter can be reduced, the same frequency Since electromagnetic induction noise consisting of components cannot be reduced, even if the power transmission line or distribution line is disconnected and the phase is lost, the minute current component is detected due to the induction noise received by the secondary circuit of the current converter. However, there is a possibility of erroneous determination that there is conduction.

  For this reason, the present inventor considered that the power harmonics are always reflected in the current waveform by observing the impedance of the power source using the harmonics, thereby confirming the conduction state on the power source side more accurately. In addition, by calculating the harmonic components of the line voltage and line current, electromagnetic induction noise with the same frequency and phase contained in each signal has the effect of canceling each other, allowing more accurate determination. I thought it was.

  By the way, with respect to electromagnetic induction noise, only voltage harmonics are observed when no current flows in a disconnected state, and it is considered that only current harmonics are observed due to induction noise. The impedance observation of this power source cannot be measured accurately due to the influence of noise only by observation for one cycle of AC, and more accurate phase loss determination is possible by performing observation over a long period of time.

In the phase loss detector of one embodiment,
In the phase loss state determination unit, the constant K2 used for the fourth condition is about 1.5.

  According to the embodiment, the fourth condition can be accurately determined by setting the constant K2 used for the fourth condition to about 1.5 in the phase loss state determination unit.

In the phase loss detector of one embodiment,
The phase loss state determination unit determines the first, second, and third conditions for each of the current waveform data of each phase for the M cycles, and sets the first, second, and third conditions to at least one. A phase failure sign determination unit that determines that a phase failure has occurred when the number of times is satisfied is provided.

  According to the above-described embodiment, when the phase loss state determination unit satisfies the first, second, and third conditions at least once, the phase loss state determination unit determines that the phase loss state determination unit is in the phase loss state. It becomes possible to respond promptly before.

  As is clear from the above, according to the present invention, when no load is connected to the secondary side of the transformer, when a separate power source is connected, and when the signal cable of the measurement circuit is white noise component or inductive noise Even when the components are superposed, it is possible to realize a phase loss detector that can accurately detect the phase loss state.

FIG. 1 is a configuration diagram of an open phase detection system using an open phase detector according to an embodiment of the present invention. FIG. 2 is a diagram showing a first open phase determination algorithm of the calculation unit of the open phase detector. FIG. 3 is a graph showing the relationship between the current value and the M value. FIG. 4 is a diagram showing a second phase loss determination algorithm of the calculation unit of the phase loss detector. FIG. 5 is a diagram showing one phase of a circuit model of a power transformer when there is almost no load (load resistance 100 MΩ). FIG. 6 is a diagram showing a waveform example of the primary side of the power transformer at substantially no load. FIG. 7 is a diagram showing a Fourier transform result of the voltage waveform of FIG. FIG. 8 is a diagram showing a Fourier transform result of the current waveform of FIG. FIG. 9 is a configuration diagram of the power receiving transformer of the power generation substation.

  The phase loss detector of the present invention will be described in detail below with reference to the illustrated embodiments.

  FIG. 1 shows a configuration diagram of an open phase detection system using an open phase detector 11 according to an embodiment of the present invention. In this phase loss detection system, as an example, a three-phase power source supplied from a receiving line or bus is connected to the primary side of the transformer TR in the substation via the transmission line L, and the phase loss detector 11 The phase loss state of the three-phase power source on the primary side of the transformer TR is detected.

  As shown in FIG. 1, the phase loss detection system of this embodiment includes a voltage converter 1 (hereinafter referred to as VT1) that converts a line voltage on the primary side of the transformer TR, and a primary side of the transformer TR. A current converter 2 for converting a phase current into a voltage (hereinafter referred to as CT2), a phase loss detector 11 for receiving a signal from the VT1 and CT2 and determining a phase loss state of the three-phase power source, and a phase loss detection A data server device 13 that receives the determination result from the detector 11 via the communication network 12, and a monitor device 14 that receives and displays the determination result from the phase loss detector 11 via the communication network 12.

  The phase loss detector 11 includes a measurement voltage converter 3 that converts a voltage on the primary side of the transformer TR converted by VT1 into a voltage signal for measurement, and a current on the primary side of the transformer TR that is converted by CT2. Current voltage converter 4 for converting the voltage signal representing the signal into a voltage signal for measurement, and A for performing A / D conversion of the voltage signal for measurement converted by the voltage converter 3 for measurement and the current voltage converter 4 for measurement A / D converter 5, waveform data memory unit 6 for storing waveform data converted into digital data by A / D converter 5, vector amount calculation unit 7 a, effective value calculation unit 7 b, and M value setting unit 7 c A phase loss state determination unit 8 for determining a phase loss state based on the vector amount data calculated by the calculation unit 7, a phase loss state determination unit 8 including the line impedance vector amount calculation unit 7d, and a phase loss state determination unit 8; Based on the judgment result Having a determination result output unit 9 for outputting a signal network 12, receives the determination result from the determination result output unit 9, a display unit 10 for displaying the determination result of the open phase state determination unit 8.

  Further, the vector amount calculation unit 7 a performs vector amount calculation based on the waveform data stored in the waveform data memory unit 6.

  Moreover, the effective value calculation part 7b calculates the effective value of each phase current for every cycle in a commercial frequency. Note that the effective value calculation unit 7b may calculate the effective value of each phase current every several cycles (every N times the waveform data).

  Further, the M value setting unit 7c sets “M value” based on the effective value of each phase current calculated by the effective value calculating unit 7b.

  Further, the line impedance vector quantity calculation unit 7d divides the vector quantity of the line voltage by the vector quantity of the same line current for each of the third to seventh harmonic components, thereby calculating the line impedance vector quantity. Calculate.

  The three-phase power supplied from the receiving line or bus of the substation is supplied to the transformer TR, and VT1 and CT2 are installed on the way.

  The voltage signal of VT1 is converted into a voltage signal of several volts or less by the measurement voltage converter 3 in the phase loss detector 11. The CT2 current signal is converted into a voltage signal of several volts or less by the measurement current-voltage converter 4 in the phase loss detector 11.

  Next, each voltage signal of the measurement voltage converter 3 and the measurement current voltage converter 4 is sampled by the A / D converter 5 corresponding to N samples per cycle (N is a positive integer) at the commercial frequency. It is sampled at a frequency and converted to a digital signal.

  The digital data converted into a digital signal by the A / D converter 5 is stored in the waveform data memory unit 6 as waveform data.

  Next, based on the waveform data stored in the waveform data memory unit 6, the vector amount calculation unit 7 a converts it into a vector amount and sends it to the phase loss state determination unit 8.

[First phase failure detection algorithm]
First, in the first phase loss determination algorithm, the phase loss state determination unit 8 determines the following [first condition], [second condition], and [third condition] every M cycles (M is a positive integer). To do. Therefore, the current waveform data of each phase is N × M. This M is called M value.

  [First Condition] In the vector amount extracted from the current waveform data of each phase for M cycles extracted by the vector amount calculation unit 7a, the absolute value of the same “1 phase” vector amount among the three phases is always The absolute value of the vector quantity of the other phase is not more than K1 times (K1 is a constant close to zero less than 1.0, for example, about 0.03).

  [Second Condition] When the neutral point of the primary side of the transformer TR is not grounded, the vector sum of the fundamental wave components of the other two-phase currents is substantially zero, or the primary of the transformer TR When the neutral point on the side is grounded, the vector sum of the currents of the two phases and the current of the grounding line is substantially zero.

  [Third Condition] Among the three phases, the absolute value of the current vector quantity of the phase in which the absolute value of the current vector quantity is maximum is 50% or more of the charging current value including the exciting current of the transformer TR. .

  The phase loss state determination unit 8 determines the [first condition], [second condition], and [third condition] for each M cycles, and continues for the L times set in advance [first condition], [ When the [second condition] and [third condition] are satisfied, it is determined that “one phase” in the above [first condition] is in a state of phase loss.

  When the phase failure state determination unit 8 determines that “one phase” in the [first condition] is in the phase loss state, the determination result output unit 9 outputs the determination result. Further, the determination result from the determination result output unit 9 is displayed on the display unit 10, and the determination result from the determination result output unit 9 is transmitted to the data server device 13 and the monitor device 14 via the communication network 12.

In the vector amount calculation unit 7a, a discrete Fourier transform method is used for conversion from waveform data to vector amount data. This is the waveform data
sin (2πn · kΔt / T) and cos (2πn · kΔt / T)
Where n is the order of the harmonic component vector quantity (1 for the fundamental vector)
k: 0, 1, 2,..., N-1 (N = T / Δt)
Δt: Sample time interval
T: Multiply by multiplying by time width to obtain the sine component An and cosine component Bn of the nth harmonic component of the waveform data, and use them as vector quantities. For this, a method called DFT (Discrete Fourier Transform) for obtaining individual components (see (Equation 1) described later) may be used, or a method called FFT (Fast Fourier Transform) for obtaining all frequency components at once. May be used.

  Naturally, in order to avoid an error due to the phase at the time of waveform data cut-out and the waveform to be observed not matching any of the FFT BIN frequencies, a sideband band is multiplied by a window function. The width may be suppressed to a certain value or less, and at the time of calculating the effective value, it may be calculated by a pyragoras sum including sidebands around the main spectrum. In addition, FFT can be performed in order to shorten the calculation time, and then the same effect as that obtained by performing simple processing on the FFT calculation result and multiplying the window function can be obtained, or by using the recursive DFT method. You may obtain | require the result of FFT on a sequential moving average.

  Although it is a known fact about the window function, when taking the data of the time width T and performing the Fourier transform, it is synonymous with multiplying the rectangular wave window function of the same time width, and the head portion and the tail portion of the data If there is a difference between the values, it is recognized that there is a repetitive waveform component having a time width T corresponding to the difference, and a frequency component not included in the original waveform appears.

  Therefore, the first and last parts of the data are compressed by multiplying by the window function, and the frequency spectrum data resulting from the Fourier transform that exceeds the separately determined noise level is centered on the largest frequency spectrum data. The frequency spectrum data exceeding the noise level must be included in (Equation 2), which will be described later, within a few lines before and after the maximum.

  If the frequency of the fundamental wave component is known, the frequency of the harmonic component can also be calculated as an integer multiple of the frequency, and the harmonic component can be calculated from several spectra around the frequency of each harmonic. .

ただし、△ｔ ：波形のサンプリング時間間隔
ｖ(k△t) ：観測値の第ｋサンプル目の値
ｗ(k△t) ：窓関数 The mth spectral component of the result of the Fourier transform can be calculated by the following (Equation 1).

Where Δt: waveform sampling time interval
v (k △ t): Value of the kth sample of the observed values
w (k △ t): Window function

For example, in the case of a Hanning window,
W (kΔt) = 0.5 × (1-cos (2πkΔt / T))
However, T: It is a function like time width. Δt / T is
Δt / T = 1 / (N × M)
Where N is the number of samples per cycle at the commercial frequency
M: Total number of data samples to be subjected to Fourier transform, which is the number of commercial frequency cycles.

(ただし、Ｎ＝６４サンプル／１サイクル) For example, when the fundamental frequency is 50 Hz, the number of cycles for extracting the vector quantity is M = 4, and the number of samples per cycle at the commercial frequency is N = 64 samples / 1 cycle, the waveform data is 64 × 4 = Sampled over 256 samples, four commercial frequency cycles. At this time, the frequency spectrum of the result of the Fourier transform is one for every 12.5 Hz. If the 0 Hz component is the 0th, the 4th is 50 Hz, which depends on the form of the window function. Several spectrums before and after are fundamental spectrum components. The effective value V _rms of the fundamental wave component is calculated by the following (Expression 2) from the fourth and subsequent several spectra.

(However, N = 64 samples / cycle)

  The above (Equation 1) shows the case where the voltage vector quantity is obtained based on the voltage waveform data as an example. However, in the case of calculating the current vector quantity, the same calculation formula is used only by replacing the data with the current waveform data. Can do.

  When the vector amount can be extracted, the next phase failure determination is performed.

とする。そして、欠相判定は、

(ただし、Ｋ１は０.０３程度の係数)
で行う。なお、係数Ｋ１は１.０未満の値を適宜設定してよい。 First, the phase loss determination method of the phase loss state determination unit 8 will be described. The extracted current vector quantities are arranged in the order of their absolute values,

And And the phase loss judgment is

(However, K1 is a coefficient of about 0.03)
To do. The coefficient K1 may be appropriately set to a value less than 1.0.

This is sufficient for normal phase loss judgment, but the object of the present invention is to provide a state in which no load is connected to the secondary side of the transformer TR (only with a slight excitation current or charging current of the transformer TR). ) To detect phase loss. Therefore, it is detected that a normal charging current flows in the phase with the maximum current ([third condition]). Although the detection level is about 50% of the charging current value, it may not be strict. Next, in order to confirm that there is no false detection, it is confirmed that the condition that the sum of the received currents of the healthy phase including the ground current I ₀ ≈0 is satisfied ([second condition]). The direction of the current flowing into the transformer TR is all positive and the polarity is unified.

  The number of data required for the determination of the phase loss state is set by the number of commercial frequency cycles (M value).

  In addition to the extraction of the vector quantity by the vector quantity calculation unit 7a, the effective value of each phase current is calculated by the effective value calculation unit 7b every cycle (or every several cycles) at the commercial frequency, and the magnitude is determined. A value (M value) expressing the acquisition time width of the waveform data required for the above in terms of the number of cycles of the commercial frequency is determined.

  This M value is changed between 3 cycles and about 3000 cycles. When the effective current value of the phase with the largest effective value of each phase current is small, the M value is set large and observed for a long time (equivalent to 60 seconds when M = 3000 at a commercial frequency of 50 Hz). When the value is large, the M value is decreased and observed for a short time (corresponding to 60 msec when M = 3 at a commercial frequency of 50 Hz) and adjusted so that the determination is possible.

As an example, the M value may be determined by the following (Equation 3).
M = Int [M _min · exp {ln (M _max / M _min ) · (I _teikaku −I) / (I _teikaku −I _reiji )}]] (Equation 3)
Where Int (x): integer part of x
M _min : Minimum value of M value
M _max : Maximum value of M value
I _teikaku : Rated current value on the primary side of transformer TR
I _reiji : Excitation current value on the primary side of transformer TR
I: Current value of the phase with the largest effective value
(For example, M _max = 3000 (equivalent to 60 seconds at 50 Hz commercial frequency), M _min = 3)
Since the M value does not need to be set precisely, for example, current values I ₃ , I ₃₀ , I ₃₀₀ , (I ₃ > I ₃₀ > I ₃₀₀ ) corresponding to each of 3 cycles, 30 cycles, and 300 cycles are set. The current value may be set to 3 cycles when the current value is I ₃ or more, 30 cycles when the current value is less than I ₃ and I ₃₀ or more, and 300 cycles when the current value is less than I ₃₀ and I ₃₀₀ or more.

  Here, if the M value is changed to M ′ during data collection of N × M samples, if N × M ′ samples are reached, the data of N × M ′ samples from the end is used. Extract vector quantities.

  In the operating state, when the phase failure determination is made while also satisfying the condition of the total sum of the received currents = 0, it is determined that the phase having the smallest current effective value is in the phase loss state, and the determination result is output to the determination result output unit 9. And the determination result is displayed on the display unit 10 or transmitted via the communication network 12.

  FIG. 2 shows a flow of the first phase loss determination algorithm of the calculation unit 7 of the phase loss detector 11. Further, the graph of FIG. 3 shows the characteristic of the M value according to the above (Equation 3).

  In the first open phase determination algorithm, first, the effective value of each phase current is obtained from the waveform data of one cycle (N samples) of the phase current Ia, Ib, Ic on the primary side of the transformer TR in the processing block 101 shown in FIG. Is calculated (effective value calculation unit 7b). Note that the effective value of each phase current may be calculated from waveform data for several cycles.

  Then, based on the effective value of each phase current calculated in the processing block 101, an “M value” is set in the processing block 102 (M value setting unit 7c).

At this time, M = M _min (eg, “3”) at the rated load, and M = M _max (eg, “3000”) at no load (see FIG. 3).

  Further, in the processing block 103, using the “M value” set in the processing block 102, each of N × M (for M cycles) waveform data of the phase currents Ia, Ib, and Ic on the primary side of the transformer TR is used. The vector quantity of the fundamental wave component of the phase current is extracted (vector quantity calculation unit 7a).

の順に並べ替える。 Next, in the processing block 104, the vector amount of the fundamental wave component of each phase current extracted in the processing block 103 is determined from the one having a large absolute value (that is, the magnitude)

Sort in the order.

(Ｋ１は０.０３程度の係数)
であるとき、欠相状態の判定に関わる[第１条件]を満たす。 In process block 105,

(K1 is a coefficient of about 0.03)
Is satisfied, the [first condition] related to the determination of the phase loss state is satisfied.

(ただし、Ｉ₀は接地電流)
であるとき、接地電流Ｉ₀も含めた健全相の受電電流の総和≒０の判定すなわち電流ベクトル和の判定に関わる[第２条件]を満たす。 In processing block 106,

(However, I ₀ is ground current)
Is satisfied, the sum of the received currents of the healthy phase including the ground current I ₀ ≈0, that is, the [second condition] related to the determination of the current vector sum is satisfied.

であるとき、稼働中であるとして[第３条件]を満たす。ここで、励磁電流は、変圧器の一次側の任意の一相における通常時の励磁電流を含めた充電電流値である。
In processing block 107,

Is satisfied, the [third condition] is satisfied. Here, the exciting current is a charging current value including the normal exciting current in an arbitrary one phase on the primary side of the transformer.

  In the logical block 108, an AND (logical product) condition of the [first condition], [second condition], and [third condition] is determined.

である相が欠相状態にあると判定する(欠相状態判定部８)。このようにして欠相状態にあると判定すると、処理ブロック１０９から、欠相状態にあることを表す信号を出力する(第１判定結果出力)。ここで、欠相状態にある相の情報を出力するようにしてもよい。 Next, in the processing block 109, when the determination result for every M cycles satisfies the [first condition], [second condition], and [third condition] continuously L times in advance, that is, AND When the result of (logical product) is “true”, the vector quantity with the smallest absolute value of [first condition], ie,

Is determined to be in an open phase state (open phase state determination unit 8). When it is determined in this way that the phase is lost, the processing block 109 outputs a signal indicating that the phase is lost (first determination result output). Here, information on a phase in an open phase state may be output.

  In the logical block 111, the AND (logical product) result when the [first condition] and the [third condition] are satisfied and the [second condition] is not satisfied is "true" every M cycles. Outputs that determination is impossible. In other words, if [Total Condition] (Open-Phase Condition) and [Third Condition] (Operating Condition) are satisfied, but the current sum of [Second Condition] is not substantially zero, it cannot be determined due to noise. The signal which represents is output (1st determination impossible output).

を抽出する。この処理ブロック１１０で抽出された接地電流Ｉ₀の基本波成分のベクトル量は、処理ブロック１０６にて用いられる。ここで、変圧器ＴＲの一次側の中性点が非接地の場合は、接地電流Ｉ₀＝０とする。 Incidentally, if the neutral point of the primary side of the transformer TR is grounded, at processing block 110, the fundamental wave of the ground current I ₀ from the waveform data of N × M pieces of ground current I ₀ (M cycles) Vector quantity of components, ie

To extract. The vector quantity of the fundamental wave component of the ground current I ₀ extracted in the processing block 110 is used in the processing block 106. Here, when the neutral point of the primary side of the transformer TR is not grounded, the ground current I ₀ = 0 is set.

  In the first phase loss determination algorithm, if the condition of the sum total of the received currents of the healthy phase is not satisfied in spite of the operation state, it is not in the phase loss state or because of induced current noise or the like. On the other hand, it is determined by the second phase loss determination algorithm based on the amount of line impedance vector on the power source side due to the harmonics that the phase loss cannot be correctly determined by the vector amount calculation of the commercial frequency.

[Second phase failure detection algorithm]
Next, a description will be given of a second open phase determination algorithm that can be determined correctly when the condition of the sum of the received currents of the healthy phases is not satisfied.

  FIG. 5 shows one phase of the circuit model of the power transformer TR at substantially no load (load resistance value 100 MΩ). In FIG. 5, R1 is a load resistance, R2 is a resistance of the transmission line L, E is a power source, C1 is a grounding capacity on the primary side of the transformer TR, and C2 is a grounding capacity on the secondary side of the transformer TR.

  In the circuit model of FIG. 5, the voltage effective value on the primary side of the transformer TR is 550 kV / √3, the voltage value on the secondary side of the transformer TR is 66 kV, and the secondary side of the transformer TR is substantially unloaded. (Load resistance value 100 MΩ), and it is designed so that the exciting current of the transformer TR is about 0.1 A and about 0.1% of the rated current value. The excitation current is easily affected by the hysteresis characteristics of the core material of the transformer TR, and the current waveform on the primary side when the load current is approximately 0 A is a distorted sinusoidal waveform as shown in FIG. Is as shown in FIG.

  FIG. 6 shows an example of the waveform on the primary side of the power transformer at substantially no load. In FIG. 6, the horizontal axis represents time [sec], the vertical axis represents branch current (phase current) [A] and node-to-node potential difference (line voltage) [V], and the bold curve represents the voltage waveform, The thin line curve shows the current waveform.

  FIG. 7 shows the Fourier transform result of the voltage waveform of FIG. In FIG. 7, the horizontal axis represents the order, and the vertical axis represents the node-to-node potential difference (voltage between lines) [V] (bar graph) and the phase angle [deg] (line graph).

  FIG. 8 shows the Fourier transform result of the current waveform. In FIG. 8, the horizontal axis represents the order, and the vertical axis represents the branch current (phase current) [A] (bar graph) and the phase angle [deg] (line graph), which are the magnitudes of the components for each order.

  Since the third harmonic component is the largest among the harmonic components excluding the fundamental component from FIG. 8 and has the opposite phase to the fundamental component flowing into the transformer TR, the third harmonic component is connected to the power supply side from the transformer TR. It can be seen that

  For example, the line impedance vector quantity is obtained by dividing the line voltage vector quantity of the third harmonic component by the homogeneous line current vector quantity.

  The number of samples of the original data necessary for extracting the vector amount is N × M, which is the same as that in the first phase loss determination algorithm.

の順に並べ替える。 From this line impedance vector quantity with a large absolute value,

Sort in the order.

(ただし、Ｋ２は１.５程度の係数)
の条件を満たすときにＺ_maxの線間と、Ｚ_midの線間に共通に含まれる相が欠相状態にあると判定する。なお、係数Ｋ２は１.０以上の値を適宜設定してよい。

(However, K2 is a coefficient of about 1.5)
When the above condition is satisfied, it is determined that the phase commonly included between the Z _max line and the Z _mid line is in an open phase state. The coefficient K2 may be appropriately set to a value of 1.0 or more.

  FIG. 4 shows a flow of the second phase loss determination algorithm of the calculation unit 7 of the phase loss detector 11.

  In the processing block 201 shown in FIG. 4, using the “M value” set in the processing block 102, N × of the line voltages Vab, Vbc, Vca and the line currents Iab, Ibc, Ica on the primary side of the transformer TR. Vector quantities of fundamental wave components and third to seventh harmonic components of each line voltage and each line current are extracted from M (M cycles) waveform data.

とすると、線間電流Ｉab,Ｉbc,Ｉcaのベクトル量は、

により求める。 Next, the processing block 202 calculates the line impedance vector quantity by dividing the vector quantity of the line voltage by the vector quantity of the line current of the same order for each of the third to seventh harmonic components (line to line Impedance vector quantity calculation unit 7d). Here, the vector quantities of the phase currents Ia, Ib, Ic are

Then, the vector quantities of the line currents Iab, Ibc, Ica are

Ask for.

の順に並べ替える。 Then, in the processing block 203, one of the harmonic components having a phase opposite to the fundamental wave component of the third to seventh order line impedance vector quantities is selected, and the line impedance of the harmonic component is selected. From the line where the absolute value (i.e. size) of the vector quantity is large,

Sort in the order.

(ただし、Ｋ２は１.５程度の係数)
であるとき、欠相状態であると判定する。 Next, at process block 204,

(However, K2 is a coefficient of about 1.5)
When it is, it is determined that the phase is in an open phase.

  Then, the logical block 205 determines an AND (logical product) of the first non-determinable output indicating that the first non-phase determination algorithm cannot be determined and the condition that the processing block 204 is in the non-phase state (definite phase determination). Part 8).

の２つの線間インピーダンスベクトル量に共通に含まれる相が欠相状態にあると判定する(欠相状態判定部８)。そして、処理ブロック２０６から、２つの線間インピーダンスベクトル量に共通に含まれる相が欠相状態にあることを表す信号を出力する((判定結果出力部９からの第２判定結果出力)。 Next, in the processing block 206, when the determination result for each M cycle is “true” as the AND (logical product) result of the logical block 205 continuously for a predetermined L times,

It is determined that the phase that is commonly included in the two line impedance vector quantities is in an open phase state (open phase state determination unit 8). Then, the processing block 206 outputs a signal indicating that the phase that is commonly included in the two line impedance vector quantities is in an open phase state ((second determination result output from the determination result output unit 9)).

  In the phase loss detector 11 configured as described above, the secondary side of the transformer TR observes the waveform for a relatively long time (for example, about 10 seconds to 1 minute) when there is no load, and detects the presence or absence of the phase loss state. However, when a load is connected, it is possible to easily detect an open phase state in a short time with a larger load current. In such a case, it must be able to be determined in a short time, but since the current is large and the ratio of the observed waveform to the error of the instantaneous value (referred to as the S / N ratio) increases, it can be determined in a short measurement. is there.

  Further, according to the phase loss detector 11, when a load is not connected to the secondary side of the transformer TR, when a separate power source is connected, and when a white noise component or induction noise is present in the signal cable of the measurement circuit. Even when the components are superposed, the phase loss state can be accurately detected.

  In addition, the phase loss state determination unit 8 can detect the phase loss state more accurately by setting the constant K1 used for the [first condition] to about 0.03.

  Further, since the determination result output unit 9 displays and transmits the determination result of the phase loss state determination unit 8 to the outside, it is possible to notify the detection result of the accurate phase loss state. It should be noted that one of the display of the determination result of the phase loss state determination unit 8 and the transmission to the outside may be performed.

  Further, when the [first condition] of the phase loss determination and the [third condition] of the operation determination are satisfied, but the total of the current vector amounts does not satisfy the [second condition] of zero, the line impedance vector amount The line having the next largest absolute value with respect to the line having the next smallest absolute value among the three line impedance vector quantities calculated by the calculation unit 7d (between a pair of healthy lines not disconnected) ( A common phase included between two lines with a large absolute value when the absolute value of the line between the two sets including the phase that has lost phase is equal to or greater than K2 times (K2 is a constant exceeding 1.0). By the [fourth condition] that the phase is in the phase loss state, the determination of the presence or absence of the phase loss state can be supplemented, and more reliable detection is possible.

  The phase loss detector 11 of this embodiment is intended to detect a minute excitation current by observing for a long time, but although the random noise generated in the signal line on the secondary side of CT2 can be reduced, the same frequency component Therefore, even if the transmission line or distribution line is disconnected and the phase is lost, a small current component is detected by the influence of the induction noise received by the secondary circuit of CT2. There is a possibility of erroneous determination.

  For this reason, the present inventor observes the impedance of the power supply using harmonics, and the voltage harmonics are always reflected in the current waveform, whereby the conduction state on the power supply side can be confirmed more accurately. In addition, by calculating the harmonic components of the line voltage and line current, electromagnetic induction noise with the same frequency and phase contained in each signal has the effect of canceling each other, allowing more accurate determination. is there.

  By the way, with respect to electromagnetic induction noise, only voltage harmonics are observed when no current flows in a disconnected state, and it is considered that only current harmonics are observed due to induction noise. The impedance observation of this power source cannot be measured accurately due to the influence of noise only by observation for one cycle of AC, and more accurate phase loss determination is possible by performing observation over a long period of time.

  In addition, the fourth phase can be accurately determined by setting the constant K2 used for the fourth condition to about 1.5 in the phase loss state determination unit 8.

  The phase loss state determination unit 8 includes a phase loss sign determination unit that determines that a phase loss is detected when the [first condition], [second condition], and [third condition] are satisfied at least once. Also good. In this case, it is possible to respond promptly before the phase failure state is reached by determining the phase loss indication by the phase loss indication determination unit.

  According to the phase loss detector of the present invention, even when the secondary side of the transformer TR is unloaded, it is possible to monitor the phase loss on the primary side of the transformer TR in the presence or absence of a weak charging current of about the exciting current. When the current signal is weak, by increasing the measurement time up to about 1000 times and increasing the number of data samples, the random noise is reduced and the measurement accuracy is increased. In addition, for noise that is not reduced even when the number of samples is increased, such as inductive noise caused by a current signal that runs parallel to the signal line on the secondary side of CT2, the second open phase determination algorithm of the present invention can be used to transform voltage. Because of the hysteresis characteristics of the core of the transformer TR, the phase loss state can be reconfirmed by using the line impedance vector quantity as seen from the power supply side obtained from the third to seventh harmonic components included in the excitation current. Therefore, it is possible to perform determination with higher accuracy.

  Further, according to the present invention, when the current signal is weak, it is possible to make a highly accurate determination by increasing the measurement time up to about 1000 times, and when the current signal suddenly increases, the measurement time is automatically set. Therefore, the determination can be made in several cycles of the AC signal in the shortest time.

  In the above embodiment, the phase loss detector that performs the determination of the phase loss state using the first phase loss determination algorithm shown in FIG. 2 and the second phase loss determination algorithm shown in FIG. 4 and the phase loss detection provided therewith Although the system has been described, the phase loss detector is not limited to this, and the present invention may be applied to a phase loss detector that determines the phase loss state using only the first phase loss determination algorithm.

  In the above embodiment, the phase loss detector 11 including the determination result output unit 9 that displays the determination result of the phase loss state determination unit 8 and transmits the result to the outside has been described. Not necessary.

  The transformer of the emergency power unit of the conventional power plant is designed so that the exciting current becomes extremely small because it does not normally operate, and the exciting current is about 0.1 A even when the line voltage is 550 kV. On the other hand, since the short circuit current is several thousand A, a significant figure of about 5 digits is required on the measurement side. Since such a short-circuit current of several thousand A cannot be passed through the measurement system as it is, a converter such as a CT is an indispensable requirement in the field. For example, in order to change the current from 4,000 A to 5 A, the current transformation ratio is 800: 1. CT is required. In this case, when the primary side current of the CT is 0.1 A, the secondary side current is 125 μA, and it is difficult in terms of accuracy to monitor such a minute current in a protective relay room several hundred meters away.

  On the other hand, in the phase loss detector of the present invention, the current value of the CT secondary side current is accumulated for several tens of seconds, and the vector quantity of the current of each phase is extracted by DFT. The phase loss can be determined from the secondary current of the CT that has been reduced to.

  When the current to be measured is about 125 μA, when several A of adjacent CT current flows, if the cable is running in the same wiring duct for several tens of meters, commercial frequency induction Noise (fundamental wave component) is superimposed on the secondary current of the CT being measured. In order to reduce the influence of such inductive noise, the open-phase detector of the present invention checks the logical condition that should naturally be satisfied so that the vector sum of each phase current and zero-phase current is substantially zero, and satisfies that condition. If not, divide the line-to-line complex voltage (vector quantity of the line voltage) of the harmonic component by the line-to-line complex current (vector quantity of the line current) to obtain the line impedance vector quantity. Since the determination is performed, the induction noise of the commercial frequency is canceled by the calculation by the interline element and can be effectively reduced.

  Although specific embodiments of the present invention have been described, the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Voltage converter 2 ... Current converter 3 ... Measurement voltage converter 4 ... Current / voltage converter for measurement 5 ... A / D converter 6 ... Waveform data memory part 7 ... Calculation part 7a ... Vector quantity calculation part 7b ... RMS value calculation unit 7c ... M value setting unit 7d ... Line impedance vector quantity calculation unit 8 ... Phase loss state determination unit 9 ... Determination result output unit 10 ... Display unit 11 ... Phase loss detector 12 ... Communication network 13 ... Data server Device 14 ... Monitor device TR ... Transformer

Claims (6)

A / D conversion is performed on a signal representing three-phase current on the primary side of a transformer connected to a transmission line or distribution line at a sampling frequency corresponding to N (N is a positive integer) per cycle at a commercial frequency. An A / D converter;
A vector amount calculation unit for calculating a current vector amount of each phase on the primary side of the transformer from the current waveform data of each phase A / D converted by the A / D converter;
Based on the current waveform data of each phase, an effective value calculation unit that calculates an effective value of each phase for each of the N or N multiple times the current waveform data;
A phase loss state determination unit for determining a phase loss state on the primary side of the transformer based on the calculation result of the vector amount calculation unit;
The vector quantity calculation unit is
A Fourier transform operation is performed over the current waveform data of each phase for M cycles (M is a positive integer) at the commercial frequency, and the magnitude of the fundamental wave component of the current of each phase on the primary side of the transformer A vector quantity consisting of a phase angle is extracted every M cycles,
The phase loss state determination unit is
In the vector quantity of the fundamental wave component of the current of each phase for the M cycles extracted by the vector quantity calculation unit, the absolute value of the same "1 phase" vector quantity among the three phases is the vector of the other phase. A first condition that the absolute value of the quantity is K1 times or less (K1 is a constant less than 1.0);
When the neutral point on the primary side of the transformer is ungrounded, the vector sum of the fundamental wave components of the other two-phase currents is substantially zero, or the neutral point on the primary side of the transformer When the point is grounded via a ground line, a second condition that the vector sum of each of the currents of the two phases and the current of the ground line is substantially zero;
Charging the absolute value of the vector of the phase of the current absolute value of the vector of current among the three phases is in the maximum, including the exciting current of the normal time in the primary side any one phase of the transformer The third condition that the current value is about 50% or more is determined every M cycles, and the first, second, and third conditions are continuously set L times (L is a positive integer) continuously. When satisfying the above, it is determined that the above-mentioned “one phase” is in an open phase state, and
For each of the N current waveform data calculated by the effective value calculation unit, the value of M is set to a larger value as the effective value of the phase having the maximum effective value among the three phases decreases. An open-phase detector, comprising: an M value setting unit that sets the value of M to a smaller value as the effective value of the phase having the maximum effective value increases. The phase loss detector according to claim 1,
In the phase loss state determination unit, the constant phase K1 used for the first condition is about 0.03. The phase loss detector according to claim 1 or 2,
A phase loss detector comprising a determination result output unit that displays at least one of the determination result of the phase loss state determination unit and transmission to the outside. In the open phase detector according to any one of claims 1 to 3,
The A / D converter is
A / D conversion is performed on a signal representing three line voltages on the primary side of the transformer at a sampling frequency corresponding to N per cycle at the commercial frequency,
The vector quantity calculation unit is
A Fourier transform operation is performed from the line voltage waveform data A / D converted by the A / D converter to the line voltage waveform data for M cycles at the commercial frequency, and the primary side of the transformer Extracting the vector quantity consisting of the magnitude and phase angle of the fundamental wave component and third to seventh harmonic components of each line voltage,
Any of the third to seventh harmonic components based on the fundamental wave component of each line voltage and the third to seventh harmonic component vector quantities obtained by the vector quantity calculation unit. A line impedance vector amount calculation unit for calculating three line impedance vector amounts as viewed from the primary side of the transformer from one to the power source side for each M cycles,
The phase loss state determination unit is
Of the three line impedance vector quantities calculated by the line impedance vector quantity calculation unit, the absolute value between the lines with the next largest absolute value is K2 times (K2 is the absolute value between the lines with the smallest absolute value). And the first, second, third, together with a fourth condition that a common phase included between two lines having a large absolute value is in an open phase state. When the condition is determined every M cycles and the first, third, and fourth conditions are satisfied and the second condition is not satisfied for L consecutive times, the “one phase” is positively missing. An open-phase detector, characterized in that it is determined to be in a phase state. The phase loss detector according to claim 4,
In the phase loss state determination unit, the constant phase K2 used for the fourth condition is about 1.5. In the open phase detector according to any one of claims 1 to 5,
The phase loss state determination unit determines the first, second, and third conditions for each of the current waveform data of each phase for the M cycles, and sets the first, second, and third conditions to at least one. A phase loss detector comprising a phase loss sign determination unit that determines a phase loss sign when the number of times is satisfied.

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